Q. 515.0( 1 Vote )

If the focus of a parabola is (0, –3) and its directrix is y = 3, then its equation is
A. x2 = –12y

B. x2 = 12y

C. y2 = –12x

D. y2 = 12x

Answer :

As focus lies on y – axis,


Equation is x2 = 4ay or x2 = -4ay,


Focus has a –ve co = ordinate, so equation is x2 = -4ay,


Co – Ordinate of focus = (0, -a)


-a = -3


a = 3


As per the equation,


x2 = -4ay


x2 = -4 (3) y


x2 = -12y


Hence, the required equation is x2 = -12y.


Option (A) is the answer.

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